Transcript
Anti-lock Braking System and it’s
Shaheem TMReg. No. 90012064
DOI , CUSAT
Advancements
Overview
Introduction What is ABS Timeline of ABS Motivation for development Simple hydraulic braking system Principles of ABS Components Working Types Advancements Advantages & Disadvantages summary
Introduction
Conventional braking system - Wheel lockup Reduces steering ability - vehicle slides out of control
Anti-lock Braking system (ABS) – Driver can break hard- No locking of wheels
What is ABS ? Anti-lock braking system (ABS) - automobile safety
system Prevent wheel locking Skidding wheel - less traction than a Non-skidding wheel Anti-lock brakes benefit
Can stop faster Steer while you stop
Preventing skiddingMaintain traction
Timeline
1929 : ABS first developed for aircraft by the French automobile developer Gabriel Voisin 1936: German company Bosch patented “Apparatus for preventing lock-braking of wheels in a motor vehicle”1936-: Bosch and Mercedes-Benz partner - R&D into ABS1972: WABCO partners with Mercedes-Benz developing ABS for trucks1978: First production-line ABS into Mercedes and BMW vehicles1981: 100,000 Bosch ABS installed1985: First ABS installed on US vehicles
1986: 1M Bosch ABS installed.1987: Traction control - with ABS 1989: ABS hydraulic unit combined with standard hydraulic brake unit1992: 10M Bosch ABS installed1995: Electronic Stability - with ABS and TCS - for passenger cars1999: 50M Bosch ABS installed2000: 6 of 10 new cars on the road are ABS equipped2003: 100M Bosch ABS installedPresent: Almost all new cars have ABS
More features – ESP – EBD – Cruise control – Auto Brake Assist
Motivation for ABS development
Under hard braking – Ideal system should
Provide the shortest stopping distances on all surfaces
Maintain vehicle stability and steer ability.
Comparison
Simple Hydraulic Braking system
Consists of
Master cylinder Four wheel cylinders
Simple Hydraulic Braking system
Brakes Applied
Pistons pushes
fluid from
Master cylinder
Fluid pushes pistons
of wheel
cylinders
Brake shoes
pushed out
Wheels get
locked
Vehicle stops
Principles of ABS When brakes applied- vehicle speed comes down Decrease in vehicle speed not always proportional to decrease in wheel speed Non-correspondence - Slip Magnitude measured as Slip ratio
Slip ratio = [(Vehicle speed – Wheel speed)/Vehicle speed ]× 100%
When Slip ratio = 0% : Vehicle speed corresponds exactly to wheel speedSlip ratio = 100% : Wheels locked - vehicle moves
Best braking action between 10-20%.
If vehicle speed and wheel speed is the same wheel slippage is 0%
A lock-up wheel will have a wheel slippage of 100%
(A) Slip ratio (B) Coefficient of friction between tire and road surface
(1) Icy road(2) Asphalt-paved road(3) Control range by ABS
Pressure Modulation in ABS
Release and reapply of the brake pedal – avoid locking of wheels - avoid the skidding
Antilock braking system does the same Brakes applied - pressure is quickly applied & released at the wheels - pressure
modulation Pressure modulation prevent the wheel locking ABS modulate the pressure 15 times per seconds ABS precisely controls the slip rate of wheels - ensure maximum grip force from
the tyre - ensures maneuverability and stability
ABS Components Overview
1.Hydraulic Unit2.Electronic Brake Control Module [EBCM]3.Four wheel speed sensors4.Interconnecting wiring5.ABS indicator
ABS Components Overview(1) ABS control module and hydraulic control unit (ABSCM & H/U)(2) Two-way connector(3) Diagnosis connector(4) ABS warning light(5) Data link connector(6) Transmission control module (AT models only)(7) Tone wheels(8) ABS wheel speed sensor(9) Wheel cylinder(10) G sensor(11) Stop light switch(12) Master cylinder(13) Brake & EBD warning light(14) Lateral G sensor
ABS components
ABS systems are Integrated
Non- integrated
ABS components
ABS has four Primary Components
ABS Controller ABS Speed Sensors
ABS Modulator/Valves ABS Pumps
Working of ABS
Under normal braking
Brakes applied No current flow from ECU to hydraulic unit Solenoid valves not energized – brake master cylinder pressure
reaches wheels Vehicles stops ABS not involved - Still ECU monitors each wheel for lock- up
Working of ABS
When wheel lock-up sensed
Wheel sensors senses a wheel lock-up ECU sends a current to hydraulic unit The solenoid valve gets energised Valve isolates the brake circuit from master cylinder Stops the braking pressure at wheel rising – kept it constant
Working of ABS
Still wheel deceleration is rapid
ECU sends larger current to hydraulic unit Armature of Hydraulic unit moves faster Opens a passage : Brake circuit – Master cylinder Pressure in brake caliper reduced
Working of ABS
When wheel is accelerated again
ECU stops current to Hydraulic unit De-energises the solenoid valve Pressure is build up The cycle repeats several times in a second Vehicle stops safely
Working of solenoid valve in ABS
It has 3 modes
Increase pressure Hold pressure
Decrease pressure
Solenoid 1
Pressure increase
Solenoid 2
Pressure decrease/Vent solenoid
Brake line under pressure
Brake fluid line not under pressure
Increase pressure
Solenoid 1
Pressure increase
Solenoid 2
Pressure decrease/Vent
Pressure hold
Solenoid 1
Pressure increase
Solenoid 2
Pressure decrease/Vent
Pressure decrease
Types of ABS
Three types
Four channel – Four sensor ABS Three channel – Three sensor ABS One channel – One sensor ABS
Advancements
Automatic Stability Control / Electronic Stability Control (Program) - ESP
Automatic Traction Control - ATC
Automatic Stability Control / Electronic Stability Program - ESP
Components
Yaw rate sensorESP hydraulic control unit
Steering angle sensorG sensor
Wheel speed sensorsECU
Operation
Under normal driving
ESC works in background- monitors steering & vehicle direction Determines intended direction – steering angle sensor
Determines vehicle’s actual direction- yaw sensor- wheel speed sensors Compares the obtained data
Operation
When detects a loss of steering control
Detects – Understeer or Oversteer ESC estimates direction of speed
Applies brakes to individual wheels asymmetrically Create torque about vehicle’s vertical axis- oppose skid
Brings vehicle back to control Additional operation – reduces engine power, operate transmission
Oversteer Understeer
Automatic Traction Control - ATC
Apply brakes when drive wheel attempts to spin and lose traction A secondary function of ESP
Activated when throttle input & engine torque is mismatched to road surface conditions
Automatic Traction Control - ATC
ATC intervention consists of the following
Brake force applied to one or more wheels Reduction or suppression of spark sequence to one or more cylinders
Reduction of fuel supply to one or more cylinders Closing the throttle
Components of traction control
The main hardware for traction control and ABS are same Wheel sensors
ECU ATC valve
Advantages of ABS
Reduce the stopping distance. Steer while the brakes are firmly applied.
Maintain directional stability and control over steering during braking. Safe and effective.
Automatically changes the brake fluid pressure at each wheel to maintain optimum brake performance.
ABS absorbs the unwanted turbulence shock waves.
Disadvantages of ABS
Increased braking distances under some limited circumstances cost
Maintenance cost of a car equipped with ABS is more System damage
Summary
The antilock braking system controls braking force by controlling the
hydraulic pressure of the braking system, so that the wheels do not lock
during braking.
The antilock braking system prevents wheels locking or skidding, no matter
how hard brakes are applied, or how slippery the road surface. Steering stays
under control and stopping distances are generally reduced.
References
[1] “Effectiveness of ABS and vehicle stability control systems”(PDF). Royal Automobile Club of Victoria. April 2004.[2] “Non-skid braking” Flight International. 30 October 1953. pp. 587–588.[3] “Chrysler Imperial Sure Brake system description”. ImperialClub.org[4] "Electronic Stability Control (ESC)" . nhtsa.gov[5] Heibing, Bernd (2011), Chassis Handbook Springer, ISBN9783834897893[5] "Speed With Style", Cycle World, June 1992, ISSN0011-4286
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